INFRARED STUDY OF NITROGEN MONOXIDE ADSORPTION ON PALLADIUM ION-EXCHANGED ZSM-5 CATALYSTS

The adsorption of NO at room temperature on a H-ZSM-5 catalyst exchang ed with Pd(NH3)(4)(2+) complex and activated in oxygen at 773 K has be en examined by FTIR spectroscopy. After the oxidizing treatment, the P d tetrammine complex decomposed into Pd(II) ions and/or Pd(II) hydroxy l complexes dispersed in the zeolite channels. The subsequent adsorpti on of NO at room temperature led to the reduction of Pd(II) to Pd(I) e ntities, resulting in the formation and adsorption of NO2 on H-ZSM-5. The Pd(I) entities were shown to adsorb NO and form mononitrosyl compl exes dispersed in the zeolite porosity and characterized by a single i nfrared absorption band at 1881 cm(-1). The Pd(I) mononitrosyl complex was shown to reversibly coordinate water and NO2 molecules. The resul ting nitrosyl complex was characterized by a single NO vibration band at 1836 cm(-1).